Get a piece of steel, about an inch wide, 4 inch long,
Drill hole in one end 8mm or so, get a bolt/nut so that you can bolt it down to the mech hanger really tight.
Drill a 5mm hole and put an old jockey wheel on it, play around with washers to get it inline, sorted (Y)
EDIT: Even better idea, get a new mech hanger £7 posted, www.tartybikes.co.uk I had to get one for my ET.